Give reasons:
(a) n-Butyl bromide has higher boiling point than t-butyl bromide.
(b) Racemic mixture is optically inactive.
(c) The presence of nitro group (`-NO_(2)`) at op positions increases the reactivity of haloarenes towards nucleophilic substitution reactions.

Explanation

The presence of `-NO_(2)` groups at o/p-position withdraws electrons from the benzene ring and thus facilitates the attack off the nucleophile on the haloarenes. Further, the carbanion thus formed is stabilized by resonance.